Customize thread pool defaults, avoid the caveats

threadpoolsettings.md

Customize thread pool defaults, avoid the caveats

.NET runtime allows customize default thread pool settings. There are essentially 4 values that could be customized:

• Minimum worker thread count;
• Minimum IO thread count;
• Maximum worker thread count;
• Maximum IO thread count;

And there are 4 primary APIs, 2 to read min/max, 2 to set those values:

• ThreadPool.GetMinThreads
• ThreadPool.GetMaxThreads
• ThreadPool.SetMinThreads
• ThreadPool.SetMaxThreads

For example:

These lines reads the minimum and maximum thread settings:

ThreadPool.GetMinThreads(out int workerThreads, out int completionPortThreads);
Console.WriteLine("Min Worker Threads: {0}, completion port threads: {1}", workerThreads, completionPortThreads);

ThreadPool.GetMaxThreads(out int maxWorkerThreads, out int maxCompletionPortThreads);
Console.WriteLine("Max worker threads: {0}, completion port threads: {1}", maxWorkerThreads, maxCompletionPortThreads);

Caveat - settings will fail if the min value given is greater than the max

Assuming on a box, these are the defaults

Min Worker Threads: 8, completion port threads: 1
Max worker threads: 32767, completion port threads: 1000

This would fail:

bool result = ThreadPool.SetMinThreads(32, 1001);   // Expect to return false since 1001 > 1000.
Console.WriteLine("Set #1 result: {0}", result);

Tips: a boolean is returned to indicating whether the operation succeeded or not.

To make it work, enlarge the max first:

ThreadPool.SetMaxThreads(maxWorkerThreads, maxCompletionPortThreads + 1);
result = ThreadPool.SetMinThreads(32, 1001);   // This will success, since the max of IO pool thread count is now 1001.

Tips: The set API requires 2 parameters. If you only want to change 1 value, read and pass back the original value. Just like the maximum worker thread pool thread count above.